Antigen Presenting Cell (APC): Structure and Function

Antigen Presenting Cell (armoured personnel carrier) Structure and FunctionThere ar many a(prenominal) coordination compound mechanisms employed by the immune system to destroy invading organisms, abnormal st anys and contain transmissions in order to maintain health and life sentence. Antigen imparting carrels (APC) argon some(a) of the cells that form part of these mechanisms. This essay will get a line at what APCs atomic number 18, the divergent types with role models and their unique(predicate) roles in the immune rejoinder.APCs atomic number 18 cells that take up antigens and present them to lymphocytes during an immune response (Sherwood et al, 2009). The comp angiotensin-converting enzyments of APCs that actually do the presenting be Major Histocompatibility mazyes (MHCs) rank I and Class II MHC molecules (Sompayrac, 2003). These two tangledes provide two varied path styluss of antigen presentation that stimulates different tribe of T cells to elimin ate the invading pathogen concerned. in all nucleated cells of the personify express MHC separate I molecules and are be causal agent referred to as non- pro APCs (Kropshofer et al, 2005). MHC course of instruction I molecules are like billboards that display on the surface of the cell, peptides of processed endogenous proteins (Sompayrac, 2003).The endogenous proteins could be those encoded by computer vir utilisations or para posts that bear septic the cell. The main focus of MHC physique I APCs is on events within the cell. Typically in a viral transmission system, the virus enters the cell and uses the cells own biosynthetic machinery to produce proteins encoded by viral genes (Wagner et al, 2004). Viral proteins are broken down into peptides by enzymes within the cell (proteasomes) (DeFranco et al, 2007). Following this, the peptides are carried into the endoplasmic reticulum by a TAP transporter (Sompayrac, 2003). After which MHC yr I molecules within the cell are e ssenceed with these peptides along with a sample of other normal proteins universe made by the cell. This MHC-peptide complex is and then transported to the cell surface for presentation. The protein fragments are displayed on MHC class I molecules to cytotoxic T cells (Tc) (Schindler, 1991). Having this mechanism in place relinquishs all body cells to be monitored by CD8+ve Tc cells which inspect the cells. Tc cells detect hostile peptides bound to an MHC so if a cell has been invaded by a virus or parasite, the Tc cells are alerted and respond by destroying the abnormal cell thus preventing the spread of viruses through emerge the body (DeFranco et al, 2007).MHC class II molecules are designed to present peptides to abeter T cells (Th). Unlike the MHC class I molecules, MHC class II molecules are restricted to certain cell types termed professional APCs. Their focus is on events unfolding in the outside environment so back tooth present samples of antigens derived from exog enous antigens in various parts of the body. captain APCs display class I and class II MHCs as favorously as co-stimulatory signals (Sompayrac, 2003). In order to function, T cells, both Tc and Th cells, require activation. For this to happen, T cells contain to recognise its cognate antibody in an MHC complex and they excessively need a co-stimulatory signal which fuck and be provided by professional APCs (Wellness.com, 2010). Co-stimulation is provided by a protein (B7) on APCs which interlocks with a nonher protein (CD28) on the surface of T cells.Examples of professional APCs are incited macrophages, oxygenated dendritic cells (DC) and excited B cells. DCs are the most important of the APCs as it adequate of initiating an immune response by activating nave T cells (Sompayrac, 2003). These cells are strategically located in areas of the body such as the skin, mucosal lining of lung and digestive tract where microbes are likely to enter (Sherwood et al, 2009). In normal tissues DCs are im arise, expressing hardly a(prenominal) B7 protein and MHC molecules on their surfaces so are short(p) antigen presenters. besides, when a microbe(s) invade the tissue which DCs reside, they mature. DC are specialised as they direct pattern recognition receptors on their surface which recognises common features of invading microbes such as LPS on the surface of gram negative bacteria. DCs takes up pathogens through receptor mediated endocytosis and degrade it in a lysosome (DeFranco et al, 2007). During a invasion, cytokines (TNF ) released by initiate macrophages are recognised by the DC which informs it that ingrained immune system is under attack. Cytokines bind to receptors on the DC create it to cease phagocytosis, leave the tissues (site of infection) and immigrate through the lymphatic system. Whilst travelling, the DC equips the class II MHC reserves with the antigen and excessively produces B7 co-stimulatory protein. During this sentence besides , DC upregulates the expression of class I MHC molecules as a precautionary measure that if the DC was infected by a virus or parasite at the site of infection, the antigen could be processed into protein fragments for presentation if necessary (Male, 2004). By the cadence the DC reaches the lymph thickener, it has its co-stimulatory molecules and the MHC class II- peptide complex(es) primed and ready to activate nave T cells.Lymph nodes have compartments that have bountiful supplies of B and T cells (Schindler, 1991). Whilst at the lymph node, DCs trigger the adaptational immune response by presenting antigens to CD4+ve Th cells with matching receptors (Sherwood, 2009). After which, the APC eject interleukin, a chemical which activate Th cells. Activated Th cells then secretes cytokines which stimulates the Th into rapid proliferation and differentiation into effector Th cells and holding Th cells (DeFranco et al, 2007). Memory Th cells are useful in hereafter infections by t he same pathogen whilst effector Th cells activate B cells to secrete antibodies enhancing other immune activities (Sherwood, 2009). Additionally effector Th cells and antibody molecules depart from the lymph node and enter the circulation which they then leave at the infection site. Antibodies opsonise the bacteria enhancing their uptakes by phagocytes, stimulate Natural killer cells (NK) to directly lyse the bacteria and also activate the lethal compliment system (Sherwood, 2009). CD4 +ve T-cell on the other hand activate macrophages to become to a greater extent cytotoxic.It is important that the magnitude of the immune response be in proportion to the skilfulness of the attack (Sompayrac, 2003). As previously mentioned DCs migrate to lymph nodes only when activated by battle cytokines. In a serious infection, many cytokines are released and thus more DCs are activated. Before their migration to lymph nodes, activated DCs release chemokines, a chemical which triggers precursor c ells (monocytes) to leave the blood waterway and become their replacement as DCs in (Sompayrac, 2003). These new DCs are then able to be activated and make their way to the lymph node which amplifies the response to the invasion. The new recruits of DCs are like photojournalists, the antigenic peptide which they carry to the lymph node beingness a snapshot of the infection site (Sompayrac, 2003). This is useful so if on that point are changes in the area, the take away T cell can be activated and thus elicit the immune response most suitable. If the infection is mild, there will be less cytokines produced, less DCs activated, fewer chemokines released, fewer replacements of DCs therefore the number of DCs that make their way to the lymph node will also be significantly less. Consequently the number of B and T cells that becomes activated in the lymph nodes relies greatly on the number of DCs present.As detailed in a higher place DCs play a role in the activation of macrophages . Macrophages are one of the early defences against invaders that initiate the cell mediated immune response (Schindler, 1991). Macrophages are very weak at presenting antigens as they only possess rich MHC molecules and co-stimulatory proteins when activated by battle cytokines e.g. IFN (DeFranco et al, 2007). Macrophages function in the re-stimulation of experienced T cells so they continue to partake in the fight against the pathogen (Male, 2004). They engulf pathogens that have invaded the tissues, process it use internal enzymes and present the peptides on MHC class II molecules. This continual display of antigens is recognised by Th cells which continue to established their function. Next the activated macrophage releases cytokines are previously mention that act on the DC i.e. TNF . early(a) cytokines released includes IL-1 and IL-8. IL-1 aids in the activation of B and T cells (Schindler, 1991).B cells are the third professional APC. At the counterbalance of an infecti on B cells are nave so do not play a definitive role. However throughout the course of the infection B cells become activated. Some B-cells are specific to T-independent antigen so only require binding of its receptor (BCR) to a cognate antigen for activation (Sherwood 2009). Other B-cells are specific to T-dependent antigen so after processing the antigen and displaying it on MHC class II molecules, binding of a Th cell is required for their activation. The MHC class II complex interacts with the TCR on the CD4+ Th cell which recognise the specific antigen on the B cell. Next the helpers release a chemical cognize as interleukin triggering the activation of the B cell. Activated B cells go through rapid proliferation and differentiation into memory cells and antibody producing plasma cells (Sherwood, 2009). B cells have the advantage of presenting the antigen very quickly so makes the immune response more efficient.The teaching of two different pathways of antigen presentation i. e. via MHC class I and II molecules can be rationalised in that each ultimately helps to elicit the most appropriate immune response through stimulation of the T cell the population most effective in eliminating the pathogen in question.MHC class I APCs allows for the monitor of all body cells through Tc cells whilst MHC class II APCs anticipate the help of Th cells and B cells which directs the immune response in a way that corresponds to the seriousness an infection. Through these functions, APCs ultimately helps to maintain health and life.Should Teens Be Allowed net cut back Access?Should Teens Be Allowed Internet Access?The mesh is a large market with practically everything available in it. It is a commodious network of computers planetary committed by cables and satellites. Most of the time, it is just referred to as The Net or the World Wide Web (www). The internet directly is used for multiple tasks such as receiving email, communicating with flock from all around the foundation, receive text, images, video and sound. It is a very helpful bastard for getting any education requisite. This is because it has people from all around the nut posting nurture onto the internet for the use of everybody who access the internet which is a public accessible feather for millions of people nationwide. (Young Media Australia 2008, What is the internet?)However, the internet forthwith is too widely used by tweens and is becoming an issue among our society. This is caused by different factors that may be dangerous to them. This study is to investigate whether it is best(predicate) for tweens to be allowed internet access.We may wonder who exactly are tweens? To be exact, they are individuals who are no longer children anymore yet not a teenager. This mean(a)s they would fall in the age group of amidst 11 13 years old. People are doubtful virtually giving them internet access because they may not be mature enough to differentiate what is good or bad and this may cause them to be susceptible to internet danger. Internet danger is generally caused by people who are not taught with moral ethics and try to levy damage onto tweens.Advantages of the internet for tweensOffers a wide spectrum of informationThe internet is a virtual treasure thorax full of valuable information. It has a grand amount of publications added every sidereal day and is slowly evolving as one of the greatest artificial lake of information. Any form of information from A to Z can present tense be so easily obtained just by a few clicks on the computer and tons of information show on the screen. Also, with the help of search engines on the internet, the work of hunting for information or info is minimized. Since the internet provides so much of information, it is a great source of pen for students who does research work or even just to look for information which cannot be obtained in school. Through the internet, forums can be accessed and through forums, people are able to trade information and share opinions with each other. (The Advantages Disadvantages Of The Internet n.d.)Communication with the worldThere are plenty of chat inhabit that can be used on the internet such as Live Messenger, Yahoo Messenger, Skype and so on. These chat rooms allow worldwide communication to be possible. As long as computers are connected to the internet, anybody from any part of the world can communicate online. It is very satisfied for family members who are apart to communicate with each other instantaneously without the need of using email or snail mail. (The Advantages Disadvantages Of The Internet n.d.)Saves times in completing tasksBefore internet existed, there were many tasks that took a surge of time to complete. Now with the help of internet in the modern society, the time used to complete these tasks is reduced by an uncanny amount. One example would be students using the internet to communicate with teachers online. Students who ar e slacking in studies may have extra classes with teachers through communication programs. This greatly reduces students time needed to revise on their own and yet not richly comprehend the subject. Also, assignments done can be sent to teachers via the computer with the use of email.Educational games programsGames nowadays intrigue tweens and play a big role in their lives. Computer games are constantly being played by tweens from all around the world and the internet has a huge load of these games. Specifically, educational games are the games that have positive effect on tweens. These games can provide practice in problem solving and logic and also provide practice in use of fine motor and spatial skills. Furthermore, some of the educational games require two players or more so this allows parents to occasionally play together with the child and have some family bonding. These games being fun activities help to relieve stress and help keep the thinker fresh. (Effects Of Video Game Playing On Children 2009)Risks disadvantages tweens might faceHowever good the internet might appear to be and have many advantages upon tweens, the ugly side of internet should also be reviewed carefully to actually determine whether the internet is more harmful than helpful to tweens.Access to incompatible content or informationThe internet being the treasure chest to all information, it also contains negative contents such as porn and forcefulness. Tweens who accidentally access to pornography may see images that would scar them for life and may authorizationly cause problems in their future life as these images may surface without warning. It is always internet pornography that is the first mental picture to tweens of these sexual images and the images they see causes their brain to play mind tricks on them. This causes gracious intimacy to be planted into them as something twisted and perverted and this implantation is irreversible. Ultimately, this may lead to sex ual deviancy and crime, which in turn affects their future relationships and marriages. (Children as Victims n.d.) craze also can make a huge trespass on tweens. Tweens who are exposed to violence would generally be more hot-tempered and are very likely to have antisocial fashion such as threatening aggression and assault. This is because they are brainwashed into the world of violence and cannot distinguish between fantasy and reality. They may think that violence is the only way to settle problems and that being violent shows charisma and looks macho-like. (Children And Media Violence 2009)Chance to come across internet predatorsAn internet predator is ordinarily an adult who exploits vulnerable children or tweens for sexual or abusive purposes, or also subsistn as paedophiles. These people try to do these out of the norm things to satisfy their personal fetish. They would try to use the internet as a way of getting in contact with tweens and try to prattle them to meet up. A t this point, these tweens who are not under adult watchfulness may not be mature enough to think that this is potential danger and would simply just agree to meeting with this anonymous person. This would allow tweens to be vulnerable to these internet predators to carry out their dirty activities. In some reported cases, these paedophiles have raped and killed innocent children. (What are the risks complex with my child using the internet n.d.)Become victims of cyber bullyingCyber bullying is rather common nowadays in the virtual world. What exactly does cyber bullying mean? It basically is any form of harassment that occurs via the internet. Posting fake videos on web sites, leaving mean and evil emails towards somebody are forms of cyber bullying. Tweens who are cyber bullied would feel very depressed and overwhelmed as they do not know who these people are who cyber bully them. These helpless victims would usually scram gently and be mentally imbalanced because they usually dont tell an adult rough this issue and just keep it to themselves. (What is Cyberbullying? n.d.)Be subjected to invasion of privacy, unsolicited advert financial risksThere are plenty of commercial websites on the internet that may invade privacy by requesting for personal information. Tweens may be encouraged to complete questionnaires and enter competitions that lead to the divulgence of personal information or incur unforeseen costs. Also, some sites have advertisements that encourage tweens to scram products which are costly and unnecessary for them. (What are the risks involved with my child using the internet n.d.)Addiction to the internetIt is very easy for tweens to get give to the internet because it is so interactive. With all the contents available on the internet, tweens would pick out to sit in front of a computer all day and this would cause them not to have time to finish assignments or work and decrease the time for socializing with people in person. This us ually also causes tweens to be less healthy as they would lack the exercise needed for their body. (What are the risks involved with my child using the internet n.d.)ConclusionTo look at the whole argument in an unbiased way, a relation has to be made between the advantages and disadvantages of the internet. It may appear that it is not prudent for tweens to be allowed internet access because of all the negative effects it may cause. However, from a survey carried out, majority of the people agree that tweens should be given internet access and that the advantages outweigh the disadvantages of the internet. These negative effects are avoidable and it basically comes down to the way tweens use the internet and how much they encounter about the internet. These problems may be avoided if they are guided along the way by an adult because an adult is able to differentiate whats good and whats not on the internet and teach tweens how to avoid these sites on the internet. Most of the t weens who suffer from internet disadvantages are those who are ignorant and are not taught healthy on how to utilize internet as a powerful tool.(1615 words)